Displays built from mechanical light modulators are an attractive alternative to displays based on liquid crystal technology. Mechanical light modulators are fast enough to display video content with good viewing angles and with a wide range of color and grey scale. Prior art projection displays have been designed to operate with reflective light modulator arrays. An example is the digital micromirror array, as described in U.S. Pat. No. 6,323,982 and liquid-crystal-on-silicon (LCOS) light modulator arrays, as described in U.S. Pat. No. 5,777,789. Because of the reflective nature of these prior art displays, the optical system necessarily incorporates a folded design, wherein the path for incident light (from the collector) and reflected light (to the projector) are both directed toward the same modulator surface. It is difficult to design an economical and efficient optical system for a projection display comprising reflective modulators, because of the folded nature of the optical path.
U.S. Pat. No. 4,904,061 describes a projection display based on transmissive liquid crystal modulator arrays. In this prior art projection display three independent transmissive light modulation assemblies are employed, one each for modulation of a red, green, and blue light. The separate red, green, and blue images are combined before the projection lens inside of a dichroic prism. A field sequential color method is not possible in these displays because of the relatively slow switching times inherent in the liquid crystal display. The economic advantages of this display are thus partially diminished by the need for three separate modulator assemblies.
Thus, there is a need in the art for fast, bright, low-powered mechanically actuated projection displays requiring less complicated optical paths.